The present work deals with the 17 species of the lepidopterous family Sesiidae occurring in Fennoscandia and Denmark. Also treated are a few additional species known from the adjacent N. W. European faunas and probably await discovery in the area under treatment. All species are keyed, diagnosed and illustrated in colour. The genitalia of both sexes are described and figured. Scandinavian Sesiidae are generally easily identifiable on superficial characters, but the information on genital structure may be of value in identifying aberrant or damaged specimens. Information on distinguishing characters of larvae and pupae are provided for many species. Brief description of local and total distribution of the species is given. The catalogue provides a more detailed survey of the known local distribution, based on the standard zootopographical division of the area. Information on bionomics and collecting techniques is given in greater detail than will probably be the case with most other volumes in this series. Adult Sesiids are rarely encountered in nature, and the much needed further work on Sesiid faunistics is consequently dependent on knowledge of larval habits and rearing techniques.